This invention relates generally to a label printing device and more particularly to a thermal printhead device for printing bar codes r the like on a web type of printing medium.
Printing devices which feature a thermal print head having electrically heated elements embedded therein to print data on a web of material withdrawn from a storage roll, are generally well known as disclosed for example in U.S. Pat. Nos. 3,409,902, 4,119,974, 4,145,698, 4,151,397, 4,228,441, 4,342,040, 4,376,942 and 4,507,666. In most of such prior printers, the thermal printhead is pressed under a spring bias against a printing medium backed by a platen. Also, in many of such thermal printhead devices, the platen is a roller over which the web printing medium is entrained.
Various supporting arrangements for the thermal printhead are disclosed in the foregoing patents. According to the disclosure in U.S. Pat. No. 4,507,666 to Kondo et al, aforementioned, the printhead is mounted on a pivotal frame journaled on an axis fixed to the printer body. Means for adjusting the angular orientation between the pivotal frame and the printhead carried thereon is provided in order to establish proper contact with a web backed by a roller type of platen. Feeding of the web according to the Kondo et al patent is effected by powered drive of the platen roller. Toward that end, an auxiliary roller mounted on the supporting frame holds the web in frictional drive engagement with the platen roller at a location angularly spaced from the location at which printing contact is established with the printhead. In view of the arrangement disclosed in the Kondo et al patent as well as the arrangements disclosed in the other aforementioned patents, spring bias adjustment is required to establish and maintain the proper printing contact between the thermal printhead and the platen backed web separately from the frictional drive engagement between the web and platen. Also, separate web feeding arrangements are required for previously available printers as disclosed for example in the aforementioned patents.
It is therefore an important object of the present invention to provide a portable and relatively simple printing apparatus of the thermal printhead type which is operationally reliable, without adjustment, for printing data such as bar code labels on a web type sheet of material that is fed between printing operations.
It is a further object in accordance with the foregoing object to provide a thermal printhead type of printer having a powered feed roller which acts as a platen backing the web maintained in proper contact with the thermal printhead without adjustment.
It is yet another object of the present invention to provide a thermal printhead type of printing device operatively mounted and supported by a printhead body construction that is relatively economical to manufacture and which provides easy access for servicing and maintenance purposes.